Method of Controlling a Collision Warning System Using Line of Sight

ABSTRACT

A collision warning system for a motor vehicle is disclosed. The collision warning system includes a first mode and a second mode. The system operates in the first mode when there is line of sight with a target vehicle. The system operates in the second mode where there is no line of sight with the target vehicle.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to motor vehicles and in particular to acollision warning system for a motor vehicle.

2. Description of Related Art

Collision warning systems have been previously proposed. Collisionwarning systems can alert a driver to potential hazards posed by othervehicles or objects near or on a roadway. Some collision warning systemsuse visual and/or audible messages to alert a driver of potentialcollisions.

SUMMARY OF THE INVENTION

The invention discloses an automated collision warning system. Theinvention can be used in connection with a motor vehicle. The term“motor vehicle” as used throughout the specification and claims refersto any moving vehicle that is capable of carrying one or more humanoccupants and is powered by any form of energy. The term motor vehicleincludes, but is not limited to: cars, trucks, vans, minivans, SUVs,motorcycles, scooters, boats, personal watercraft, and aircraft.

In some cases, the motor vehicle includes one or more engines. The term“engine” as used throughout the specification and claims refers to anydevice or machine that is capable of converting energy. In some cases,potential energy is converted into kinetic energy. For example, energyconversion can include a situation where the chemical potential energyof a fuel or fuel cell is converted into rotational kinetic energy orwhere electrical potential energy is converted into rotational kineticenergy. Engines can also include provisions for converting kineticenergy into potential energy. For example, some engines includeregenerative braking systems where kinetic energy from a drivetrain isconverted into potential energy. Engines can also include devices thatconvert solar or nuclear energy into another form of energy. Someexamples of engines include, but are not limited to: internal combustionengines, electric motors, solar energy converters, turbines, nuclearpower plants, and hybrid systems that combine two or more differenttypes of energy conversion processes.

In one aspect, the invention provides a method of operating a collisionwarning system in a motor vehicle, comprising the steps of: receivinginformation related to a target vehicle; determining if the targetvehicle is in a line of sight of the motor vehicle; the collisionwarning system including multiple alert modes; operating the collisionwarning system in a normal alert mode when the target vehicle is in theline of sight of the motor vehicle; operating the collision warningsystem in an enhanced alert mode when the target vehicle is not in theline of sight of the motor vehicle; and wherein the normal alert mode isdifferent than the enhanced alert mode.

In another aspect, the invention provides a method of operating acollision warning system in a motor vehicle, comprising the steps of:receiving a signal transmitted by a target vehicle; determining ameasured signal characteristic from the signal transmitted by the targetvehicle; retrieving a reference signal characteristic corresponding tothe measured signal characteristic; determining a line of sightcondition for the motor vehicle with respect to the target vehicle usingthe measured signal characteristic and the reference signalcharacteristic; operating the collision warning system in a normal alertmode when the target vehicle is in the line of sight of the motorvehicle; operating the collision warning system in an enhanced alertmode when the target vehicle is not in the line of sight of the motorvehicle; and wherein the normal alert mode is different than theenhanced alert mode.

In another aspect, the invention provides a method of operating acollision warning system in a motor vehicle, comprising the steps of:receiving information related to a target vehicle; receiving informationrelated to an intermediate vehicle; determining if the intermediatevehicle obstructs the line of sight between the motor vehicle and thetarget vehicle; operating the collision warning system in a normal alertmode when the target vehicle is in the line of sight of the motorvehicle; and operating the collision warning system in an enhanced alertmode when the target vehicle is not in the line of sight of the motorvehicle.

Other systems, methods, features and advantages of the invention willbe, or will become, apparent to one of ordinary skill in the art uponexamination of the following figures and detailed description. It isintended that all such additional systems, methods, features andadvantages included within this description and this summary, be withinthe scope of the invention, and be protected by the following claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention can be better understood with reference to the followingdrawings and description. The components in the figures are notnecessarily to scale, emphasis instead being placed upon illustratingthe principles of the invention. Moreover, in the figures, likereference numerals designate corresponding parts throughout thedifferent views.

FIG. 1 is a schematic view of an embodiment of a collision warningsystem;

FIG. 2 is a schematic view of an embodiment of alert images for acollision warning system;

FIG. 3 is a schematic view of an embodiment of a collision warningsystem displaying an informing alert image;

FIG. 4 is a schematic view of an embodiment of a collision warningsystem displaying a warning alert image;

FIG. 5 is a schematic view of an embodiment of a collision warningsystem displaying a default screen;

FIG. 6 is a schematic view of an embodiment of a collision warningsystem displaying a warning alert image;

FIG. 7 is an embodiment of a process for controlling a collision warningsystem;

FIG. 8 is an embodiment of a process for calculating a threat ofcollision between a motor vehicle and a target vehicle;

FIG. 9 is an embodiment of a process for controlling a collision warningsystem;

FIG. 10 is a schematic view of an embodiment of a signal being degradedby an obstructing building;

FIG. 11 is a schematic view of an embodiment of a signal beingpreserved;

FIG. 12 is a schematic view of an embodiment of a line of sightestimation system;

FIG. 13 is an embodiment of a process for determining line of sightconditions for a collision warning system;

FIG. 14 is a schematic view of an embodiment of a non line of sightcondition for a motor vehicle due to the obstruction posed by anintermediate vehicle;

FIG. 15 is a schematic view of an embodiment of a good line of sightcondition with respect to a target vehicle;

FIG. 16 is a schematic view of an embodiment of a non light of sightcondition;

FIG. 17 is a schematic view of an embodiment of a good line of sightcondition;

FIG. 18 is an embodiment of a process for determining line of sightconditions; and

FIG. 19 is an embodiment of a process for determining line of sightconditions.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

FIG. 1 is a schematic view of an embodiment of collision warning system100 that is configured to be used within motor vehicle 102. Collisionwarning system 100 may be a system configured to detect potentialcollisions as well as to alert a driver or passenger to potentialcollisions. For purposes of clarity, only some components of a motorvehicle that may be relevant to collision warning system 100 areillustrated. Furthermore, in other embodiments, additional componentscan be added or removed.

Collision warning system 100 can include provisions for receiving GPSinformation. In some cases, collision warning system 100 can include GPSreceiver 110. In an exemplary embodiment, GPS receiver 110 can be usedfor gathering GPS information for any systems of a motor vehicle,including, but not limited to: GPS based navigation systems.

Collision warning system 100 can include provisions for powering one ormore devices. In some cases, collision warning system 100 can includepower supply 112. Generally, power supply 112 can be any type of powersupply associated with a motor vehicle. In some cases, power supply 112can be a car battery. In other cases, power supply 112 can be anothertype of power supply available within motor vehicle 102.

Collision warning system 100 can include provisions for communicatingwith a driver. In some embodiments, collision warning system 100 caninclude driver vehicle interface 114. In some cases, driver vehicleinterface 114 can include provisions for transmitting information to adriver and/or passenger. In other cases, driver vehicle interface 114can include provisions for receiving information from a driver and/orpassenger. In an exemplary embodiment, driver vehicle interface 114 caninclude provisions for transmitting and receiving information from adriver and/or passenger.

Motor vehicle 102 may include provisions for communicating, and in somecases controlling, the various components associated with collisionwarning system 100. In some embodiments, collision warning system 100may be associated with a computer or similar device. In the currentembodiment, collision warning system may include electronic control unit120, hereby referred to as ECU 120. In one embodiment, ECU 120 may beconfigured to communicate with, and/or control, various components ofcollision warning system 100. In addition, in some embodiments, ECU 120may be configured to control additional components of a motor vehiclethat are not shown.

ECU 120 may include a number of ports that facilitate the input andoutput of information and power. The term “port” as used throughout thisdetailed description and in the claims refers to any interface or sharedboundary between two conductors. In some cases, ports can facilitate theinsertion and removal of conductors. Examples of these types of portsinclude mechanical connectors. In other cases, ports are interfaces thatgenerally do not provide easy insertion or removal. Examples of thesetypes of ports include soldering or electron traces on circuit boards.

All of the following ports and provisions associated with ECU 120 areoptional. Some embodiments may include a given port or provision, whileothers may exclude it. The following description discloses many of thepossible ports and provisions that can be used, however, it should bekept in mind that not every port or provision must be used or includedin a given embodiment.

In some embodiments, ECU 120 can include first port 121 forcommunicating with GPS receiver 110. In particular, ECU 120 may beconfigured to receive GPS information from GPS receiver 110. Inaddition, ECU 120 can include second port 122 for receiving power frompower supply 112. Also, ECU 120 can include third port 123 forcommunicating with driver vehicle interface 114. In particular, ECU 120can be configured to transmit information to driver vehicle interface114, as well as to receive information from driver vehicle interface114.

A collision warning system can include provisions for communicating withone or more vehicles using a vehicle communication network. The term“vehicle communication network” as used throughout this detaileddescription and in the claims refers to any network utilizing motorvehicles and roadside units as nodes. Vehicle communication networks maybe used for exchanging various types of information between motorvehicles and/or roadside units. An example of such a vehicular networkis a dedicated short range communication (DSRC) network. In some cases,DSRC networks may be configured to operate in the 5.9 GHz band withbandwidth of approximately 75 MHz. Furthermore, DSRC networks may have arange of approximately 1000 m.

In some embodiments, ECU 120 may include fifth port 125 that isconfigured to communicate with one or more DSRC devices. In an exemplaryembodiment, fifth port 125 may be associated with a DSRC antenna that isconfigured to transmit and/or receive vehicle information over one ormore vehicle communication networks.

Collision warning system 100 can include provisions for communicatingwith one or more components of a motor vehicle that are not associateddirectly, or indirectly with collision warning system 100. In somecases, ECU 120 may include additional ports for communicating directlywith one or more additional devices of a motor vehicle, includingvarious sensors or systems of the motor vehicle. In an exemplaryembodiment, ECU 120 may include fourth port 124 for communicating withvehicle network 140. By providing communication between ECU 120 andvehicle network 140, ECU 120 may have access to additional informationconcerning motor vehicle 102. For instance, in some cases, ECU 120 maybe configured to receive information related to various operatingconditions of a motor vehicle. Examples of information that may bereceived via vehicle network 140 include, but are not limited to:vehicle speed, engine speed, braking conditions, as well as otherparameters associated with the operating condition of motor vehicle 102.

A collision warning system can include provisions for controlling one ormore systems in a motor vehicle that may be utilized during a collision,or that can be used to help avoid a collision. For example, in someembodiments, ECU 120 may be configured to communicate with a brakeactuator to help control braking prior to, or during a collision. Inother embodiments, ECU 120 may be configured to communicate with anelectric seat belt pre-tensioner to help control a seat belt during acollision. In still other embodiments, any systems of a motor vehiclecan be controlled using ECU 120. In some embodiments, ECU 120 can beconfigured with additional ports for communicating with other systems ofa motor vehicle, including systems used during a collision. In otherembodiments, ECU 120 can be configured to communicate with these systemsusing a vehicle network. With this arrangement, a collision warningsystem can be configured to control one or more systems that may be usedto help avoid a collision or to increase the safety of one or moreoccupants during a collision.

FIG. 2 illustrates an embodiment of dashboard 200 for motor vehicle 102.Dashboard 200 may include steering wheel 202 and instrument panel 204.In some embodiments, dashboard 200 can further include center portion206. In some cases, center portion 206 can include one or more devicesassociated with an interior of a motor vehicle. Examples include, butare not limited to: audio devices, video devices, navigation devices, aswell as any other types of devices. In addition, center portion 206 canbe associated with controls for one or more systems of motor vehicle 102including, but not limited to: climate control systems and other typesof systems.

A motor vehicle can include provisions for displaying information from acollision warning system. In some embodiments, a motor vehicle caninclude a display device of some kind. In some cases, a motor vehiclecan include a video screen for displaying information from a collisionwarning system. Examples of display devices include, but are not limitedto: LCDs, CRTs, ELDs, LEDs, OLEDs, as well as other types of displays.In other cases, a display device could be a projection type displaydevice that is configured to project an image onto one or more surfacesof motor vehicle 102. It will be understood that a display device maynot be limited to a video screen or projection type display device.

In one embodiment, motor vehicle 102 can include display device 210. Insome cases, display device 210 may be associated with driver vehicleinterface 114 of collision warning system 100. In particular, displaydevice 210 may be configured to present visual information received fromcollision warning system 100. In an exemplary embodiment, display device210 may be an LCD screen.

In some embodiments, display device 210 can be disposed within centerportion 206. However, it will be understood that in other embodiments,display device 210 can be located in any portion of motor vehicle 102 aslong as display device 210 can be viewed by a driver. For example, inanother embodiment, display device 210 may be a projection type devicethat displays an image onto front window 212. In addition, while displaydevice 210 can be configured to present visual information received fromcollision warning system 100, display device 210 may be shared withother devices or systems within motor vehicle 100. For example, displaydevice 210 could also be used as a screen for a navigation system.

It will be understood that in some embodiments, a driver vehicleinterface can include additional provisions beyond a display screen. Forexample, in another embodiment, a driver vehicle interface can also beassociated with one or more input devices that allow a driver to controlvarious aspects of a collision warning system. In some cases, a drivervehicle interface can include an on/off button for turning a collisionwarning system on and off. In still another embodiment, a driver vehicleinterface can be associated with speakers for generating auditoryinformation.

A display device for a collision warning system can be configured todisplay one or more images associated with various types of alerts ofthe collision warning system. For purposes of clarity, the followingdetailed description discusses a collision warning system utilizing twodistinct alert types: informing alerts and warning alerts. Inparticular, informing alerts are used to inform a driver of nearbyvehicles or objects that could pose potential problems. In contrast, awarning alert may be issued to warn the driver of a serious threat ofcollision with a nearby vehicle or object. In other words, informingalerts inform a driver of low level collision threats, while warningalerts inform a driver of high level collision threats. In otherembodiments, any other number of alert types can be used. In some cases,three or more alert types could be issued by a collision warning system.

In the exemplary embodiment, collision warning system 100 includesinforming alert image 220 that is associated with an informationalalert. Informing alert image 220 may comprise one or more symbols oricons. In this embodiment, informing alert image 220 includesintersection symbol 222, which indicates an upcoming intersection. Inaddition, informing alert image 220 includes first arrow 224 and secondarrow 226, representing the general location and heading of motorvehicle 102 and an approaching vehicle for which there may some threatof collision. By displaying informing alert image 220, a driver isalerted to a potential collision threat with an approaching vehicle.This information may help a driver to be more aware as motor vehicle 102approaches the upcoming intersection.

In the exemplary embodiment, collision warning system 100 also includeswarning alert image 230 that is associated with a warning alert. Warningalert image 230 may comprise one or more symbols or icons. In a similarmanner to informing alert image 220, warning alert image 230 may includeintersection symbol 232, first arrow 234 and second arrow 236. Thesesymbols indicate information about an upcoming intersection as well asthe speeds and headings of motor vehicle 102 and an approaching vehicle.In addition, warning alert image 230 includes warning symbol 238. Theappearance of warning symbol 238 alerts a driver to an immediate threatposed by an approaching vehicle. This information may help a driver toavoid a collision by taking immediate action.

In addition to the two types of alerts discussed above, a display devicemay be configured to display no image when no alert has been issued bycollision warning system 100. In this embodiment, display device 210displays default screen 240 when no alert is issued. In the exemplaryembodiment, default screen 240 is associated with a blank screen ofdisplay device 210. However, in embodiments where display device 210 isused for displaying information from other systems, default screen 240may not be a blank screen. For example, in embodiments where displaydevice 210 is shared between a navigational system and collision warningsystem 100, display device 210 may continue to display images receivedfrom the navigation system until an alert is issued. Likewise, once analert has expired, display device 240 may return to displaying imagesfrom a navigation system.

Although a single image is shown for each type of alert (informingalerts and warning alerts) in the current embodiment, other embodimentscan include more than one image for each type of alert. In particular,an arrow used to indicate position and heading of a vehicle can bechanged from a straight arrow indicating the intention of a vehicle topass straight through an intersection to curved arrows in cases wherethe intention of the vehicle is to turn at the intersection. Thisarrangement can help to inform a driver as to the intentions of anapproaching vehicle. In addition, a three way intersection symbol can beused in place of a four way intersection symbol in cases where theupcoming intersection is a three way intersection. However, inembodiments using multiple images for each type of alert, it will beunderstood that some distinguishing elements may be used to indicatethat an alert is an informing alert or a warning alert. For example, asin the current embodiment, a warning symbol can be used to distinguishbetween informing alerts and warning alerts. Likewise, in some cases,informing alerts can be associated with a different color than warningalerts. In one embodiment, informing alerts can include symbols or iconscolored in yellow, while warning alerts can include symbols or iconscolored in red.

FIGS. 3 through 6 illustrate embodiments of a collision warning systemin use. As previously discussed, motor vehicle 102 includes collisionwarning system 100. In particular, motor vehicle 102 includes provisionsfor communicating with one or more vehicles using a vehiclecommunication network. Also, motor vehicle 102 includes provisions foralerting a driver of potential collisions using either informing alertsor warning alerts.

Referring to FIG. 3, motor vehicle 102 is in communication with targetvehicle 302 using vehicle communication network 304. The term “targetvehicle” as used throughout this detailed description and in the claimsrefers to any vehicle about which a collision warning system could issuean alert. Furthermore, for clarity, a vehicle possessing a collisionwarning system may be referred to as a “subject vehicle”, in contrast tothe target vehicle. In particular, motor vehicle 102 is the subjectvehicle in this embodiment.

In some cases, vehicle communication network 304 may be a DSRC network,as discussed above. In particular, using vehicle communication network304, motor vehicle 102 and target vehicle 302 may be configured toexchange various types of information including, but not limited to:vehicle position, vehicle speed, vehicle trajectory as well as othertypes of vehicle information. In addition, any type of basic safetymessage (BSM) can be exchanged via vehicle communication network 304.

In an exemplary embodiment, each vehicle operating on vehiclecommunication network 304 is presumed to have a GPS antenna to determinevehicle locations. Using vehicle location information, velocities andheadings for each vehicle can also be computed. In some cases, targetvehicle 302 may simply transmit a current GPS position and motor vehicle102 may calculate speed and heading according to the current GPSposition. In other cases, target vehicle 302 can transmit each of thesevalues independently.

In this embodiment, after receiving attributes from target vehicle 302,collision warning system 100 may determine if an alert should be issued.Since motor vehicle 102 is planning to make a left turn at intersection300 and target vehicle 302 is planning to pass straight throughintersection 300, there is potentially a threat of collision. In thiscase, collision warning system 100 issues an informing alert usinginforming alert image 220. Informing alert image 220 may include firstarrow 310 and second arrow 312, indicating the planned trajectories ofmotor vehicle 102 and target vehicle 302, respectively. By displayinginforming alert image 220, collision warning system 100 can inform adriver of motor vehicle 102 to a potential threat posed by targetvehicle 302.

Referring to FIG. 4, at a later time, target vehicle 302 is just aboutto enter intersection 300. At this point, collision warning system 100may determine that the threat of collision is very high. In this case,collision warning system 100 issues a warning alert using warning alertimage 230. Warning alert image 230 includes first arrow 314 and secondarrow 316, indicating the planned trajectories of motor vehicle 102 andtarget vehicle 302, respectively. In contrast to the informing alertimage illustrated in FIG. 3, warning alert image 230 also includeswarning symbol 318, which indicates a serious threat of collision. Bydisplaying warning alert image 230, collision warning system 100 canwarn the driver of motor vehicle 102 to a serious collision threat posedby target vehicle 302. This warning may allow the driver to alter thecurrent planned trajectory in order to avoid a collision.

In some cases, a driver may feel that a collision warning system issuestoo many alerts, especially informing alerts which may inform the driverabout situations already known to the driver. For example, in situationswhere a driver has good line of sight of a target vehicle, an informingalert displaying the location and trajectory of the target vehicle maybe seen as a nuisance. Some drivers may choose to deactivate a collisionwarning system rather than put up with these “nuisance alerts.”

A collision warning system can include provisions for reducing thenumber of alerts issued to a driver. In some embodiments, a collisionwarning system can be configured to prevent informing alerts from beingissued when a driver has good line of sight to a target vehicle. In somecases, a collision warning system can be configured to operate in two ormore alert modes. A first alert mode may be used when the driver hasgood line of sight of a target vehicle. A second alert mode may be usedwhen the driver does not have line of sight of a target vehicle. In anexemplary embodiment, the first alert mode may be referred to as anormal alert mode. The second alert mode may be referred to as anenhanced alert mode. Furthermore, during the normal alert mode, acollision warning system may issue less warnings since a driver can seethe target vehicle clearly. In contrast, the enhanced alert mode may beassociated with a higher frequency of issued alerts, since the drivercannot see the target vehicle, and thus could benefit from additionalinformation to avoid potential collisions.

Referring to FIGS. 3 and 4, motor vehicle 102 is situated behind truck340. Because of this arrangement, the line of sight from within motorvehicle 102 is reduced. For purposes of illustration, intersection 300and the surrounding area is divided into visible region 350 andnon-visible region 352. In other words, from within motor vehicle 102 adriver is able to see everything located within visible region 350, butthe driver is unable to see objects located within non-visible region352, due to the presence of truck 340 in front of motor vehicle 102.Since target vehicle 302 is within non-visible region 352, a driverinside of motor vehicle 102 cannot see target vehicle 302. In addition,a direct communication path between subject vehicle 102 and targetvehicle 302 is obstructed by truck 240. However, by using the reflectionwave path or the diffraction wave path of a communication signal,vehicle communication network 304 may still be established. In thissituation, collision warning system 100 is operated in the enhancedalert mode. In particular, as discussed above, displaying informingalert image 220 gives a driver useful information about target vehicle302 that is not considered a nuisance. In a similar manner, as targetvehicle 302 gets closer to intersection 300, collision warning system100 issues warning alert image 230. In this situation, a driver may notbe aware of an impending collision since target vehicle 302 is locatedwithin non-visible region 352 and is not in the line of sight of thedriver.

In contrast, FIGS. 5 and 6 illustrate embodiments of collision warningsystem 100 operating in a normal alert mode. In this case, the line ofsight of motor vehicle 102 is not obstructed. Also, in this case,vehicle communication network 304 is established using a direct wavepath. In particular, a driver within motor vehicle 102 can see targetvehicle 302. In this situation, collision warning system 100 maydetermine that the driver has good line of sight of target vehicle 302and therefore no informing alert is necessary. In the exemplaryembodiment, default image 240 is shown on a display screen associatedwith collision warning system.

As seen in FIG. 6, as target vehicle 302 enters intersection 300,collision warning system may determine that the threat of a collision isvery high. Therefore, at this point, collision warning system 100 mayissue warning alert image 230 even though the driver has good line ofsight of target vehicle 302.

With the arrangement discussed here, the number of alerts issued by acollision warning system can be modified according to the line of sightconditions. In particular, during normal alert mode, the collisionwarning system only issues warning alerts. In other words, the collisionwarning system only issues alerts when the threat of collision is high.In contrast, during the enhanced alert mode, the collision warningsystem may issue both informing alerts and warning alerts. Thisarrangement can help prevent deactivation of a collision warning systemfrom annoyed drivers.

As discussed above, communications between two vehicles can beestablished using direct paths as well as reflection wave paths ordiffraction wave paths. In particular, direct paths for signalsassociated with a vehicle communication network may be used when twovehicles have line of sight of one another. In addition, reflection wavepaths or diffraction wave paths for signals associated with a vehiclecommunication network may be used when there is not good line of sightbetween vehicles, since a direct path may be obstructed by one or moreobjects in such cases. With this arrangement, a vehicle communicationnetwork can be established during both good line of sight conditions andnon-line of sight conditions.

FIG. 7 illustrates an embodiment of a process for operating a collisionwarning system. In this embodiment, the following steps may be performedby ECU 120; however in some embodiments these steps may be performed byadditional systems or devices associated with motor vehicle 102 and/orcollision warning system 100. In addition, it will be understood that inother embodiments one or more of the following steps may be optional.

During step 702, ECU 120 may receive information from a target vehicle.In some cases, the information can be received from a vehiclecommunication network, such as a DSRC network. The information caninclude, in some cases, the location, speed and heading of the targetvehicle. In other cases, additional information about the target vehiclecan be received, including vehicle make, vehicle model, sizeinformation, shape information as well as other types of informationabout the target vehicle.

Next, during step 704, ECU 120 can calculate the threat of a collision.In some embodiments, the threat of collision can be associated with twoor more discrete threat levels. In some cases, the threat of collisioncan be associated with “no threat,” “low threat” or “high threat”levels. In other cases, the threat of collision can be associated withadditional threat levels. In other embodiments, the threat of collisioncan be associated with a continuous value. For example, the threat ofcollision can be a value between 0 and 100, with 0 being no threat and100 being the highest threat level. For purposes of clarity, thefollowing detailed description discusses an embodiment utilizing thethree discrete threat levels discussed above.

Following step 704, ECU 120 can proceed to step 706. During step 706,ECU 120 can determine the line of sight conditions for the driver of themotor vehicle. In particular, during step 706, ECU 120 can determinethat the driver has line of sight of the target vehicle or that thedriver does not have line of sight of the target vehicle.

Finally, during step 708, ECU 120 can control the collision warningsystem. In some cases, ECU 120 can use the threat of a collision and theline of sight conditions to determine whether or not to issue an alertas well as to determine what type of alert to issue.

FIG. 8 illustrates an embodiment of a process for calculating the threatof collision. In this embodiment, the following steps may be performedby ECU 120; however in some embodiments these steps may be performed byadditional systems or devices associated with motor vehicle 102 and/orcollision warning system 100. In addition, it will be understood that inother embodiments one or more of the following steps may be optional.

During step 802, ECU 120 can retrieve the heading, position and speed ofa target vehicle using a vehicle communication network. Next, duringstep 804, ECU 120 may estimate a vehicle collision point. The term“vehicle collision point” refers to a point at which the motor vehicleand the target vehicle would collide given current headings, positionsand speeds for both vehicles. In addition, ECU 120 may use otheravailable information for estimating a vehicle collision point, such asthe intention of one or both drivers to turn at an upcomingintersection.

Following step 804, ECU 120 may proceed to step 806. During step 806,ECU 120 may calculate the distance to the vehicle collision point. Atthis point, ECU 120 proceeds to step 808. During step 808, ECU 120retrieves a predefined informing distance and a predefined warningdistance. In other words, the predefined informing distance is adistance from the vehicle collision point within which the collisionwarning system may determine that there is a low threat of collision.Likewise, the predefined warning distance is a distance from the vehiclecollision point within which the collision warning system may determinethat there is a high threat of collision.

Following step 808, ECU 120 may proceed to step 810. During step 810,ECU 120 may determine if the current distance to the vehicle collisionpoint is less than the predefined informing distance. If ECU 120determines that the current distance to the vehicle collision point isnot less than the predefined informing distance, ECU 120 may proceed tostep 812, where ECU 120 determines that there is no threat. Otherwise,ECU 120 proceeds to step 814.

During step 814, ECU 120 determines if the current distance to thevehicle collision point is less than the predefined warning distance. IfECU 120 determines that the current distance to the vehicle collisionpoint is not less than the predefined warning distance, ECU 120 mayproceed to step 816. During step 816, ECU 120 determines that there is alow threat level. If, during step 814, ECU 120 determines that thecurrent distance to the vehicle collision point is less than thepredefined warning distance, ECU 120 proceeds to step 818. During step818, ECU 120 determines that there is a high threat level.

It will be understood that the current embodiment of a process fordetermining a threat of collision is only intended to be exemplary.Generally, any method of determining a threat level according toinformation related to a primary vehicle and a target vehicle may beused. In other embodiments, a collision warning system can use anotherprocess for determining a threat of collision. For example, in anotherembodiment, rather than calculating a distance to the vehicle collisionpoint, a time to vehicle collision point can be calculated and comparedwith a predefined informing alert time as well as a predefined warningalert time.

FIG. 9 illustrates an embodiment of a process for operating collisionwarning system 100. In this embodiment, the following steps may beperformed by ECU 120; however in some embodiments these steps may beperformed by additional systems or devices associated with motor vehicle102 and/or collision warning system 100. In addition, it will beunderstood that in other embodiments one or more of the following stepsmay be optional.

During step 902, ECU 120 may receive the threat level. In some cases,the threat level may be calculated using the method discussed above.Next, ECU 120 may receive the line of sight conditions during step 904.In particular, ECU 120 can determine if a target vehicle is within theline of sight of a driver.

Following step 904, ECU 120 can proceed to step 906. During step 906,ECU 120 may determine if there is line of sight according to the line ofsight conditions received during step 904. If there is line of sight,ECU 120 may proceed to step 908. During step 908, ECU 120 puts collisionwarning system 100 in a normal alert mode.

Following step 908, ECU 120 can proceed to step 910. During step 910,ECU 120 determines the threat level according to the threat levelreceived during step 902. If, during step 910, ECU 120 determines thatthe threat level is high, ECU 120 proceeds to step 912, where a warningalert is issued. Otherwise, if ECU 120 determines that the threat levelis low or that there is no threat, ECU 120 proceeds to step 914. Duringstep 914, no alert is issued.

Returning to step 906, if ECU 120 determines that there is no line ofsight, ECU 120 may proceed to step 916. During step 916, ECU 120 putscollision warning system 100 in an enhanced alert mode. In particular,the enhanced alert mode is a mode of collision warning system 100associated with a high frequency of informing alerts due to theinability of the driver to see the target vehicle.

Following step 916, ECU 120 can proceed to step 918. During step 918,ECU 120 determines the threat level according to the threat levelreceived during step 902. If, during step 918, ECU 120 determines thatthere is no threat, ECU 120 proceeds to step 920, where no alert isissued. If, during step 920, ECU 120 determines that there is a lowthreat, ECU 120 may proceed to step 922, where an informing alert isissued. If, during step 920, ECU 120 determines that the threat level ishigh, ECU 120 proceeds to step 912, where a warning alert is issued.

A collision warning system can include provisions for determining lineof sight conditions for a target vehicle. In some embodiments, thecollision warning system can use information associated with a vehiclecommunication network to determine line of sight conditions. In anexemplary embodiment, the collision warning system can usecharacteristics of a received signal associated with a vehiclecommunication network.

FIGS. 10 and 11 illustrate a schematic embodiment of a method ofdetermining line of sight conditions by measuring signal characteristicsassociated with a vehicle communication network. Referring to FIGS. 10and 11, motor vehicle 102 is approaching intersection 1000 along firststreet 1004. In addition, target vehicle 1002 is approachingintersection 1000 along second street 1006.

Referring to FIG. 10, building 1010 is disposed at the corner of firststreet 1004 and second street 1006. In this case, the line of sight of adriver within motor vehicle 102 is obscured by building 1010. Inparticular, a driver within motor vehicle 102 is unable to see anythinginside of non-visible region 1020, whose boundary is defined by axis1022 extending from front window 1024 of motor vehicle 102 andtangential to building corner 1026. In this situation, a driver withinmotor vehicle 102 is unable to see target vehicle 1002.

In this exemplary embodiment, motor vehicle 102 and target vehicle 1002may be in communication via a vehicle communication network, asdiscussed above. In particular, motor vehicle 102 and target vehicle1002 may be constantly transmitting information to, and receivinginformation from, one another in the form of wireless signals. In thiscase, target vehicle 1002 transmits signal 1050 to motor vehicle 102.

Due to the presence of building 1010, signal 1050 may be substantiallydegraded. In an exemplary embodiment, a collision warning system canmeasure the degradation of signal 1050 in order to determine if anobject is disposed between motor vehicle 102 and target vehicle 1002. Inthis case, due to the signal degradation caused by building 1010, thecollision warning system can determine that motor vehicle 102 does nothave line of sight with respect to target vehicle 1002.

In contrast, FIG. 11 illustrates an embodiment without a building at thecorner of first street 1004 and second street 1006. In this case, adriver within motor vehicle 102 has full line of sight and is able tosee target vehicle 1002. Additionally, signal 1052 transmitted by targetvehicle 1002 and received at motor vehicle 102 is not degraded sincethere is no obstruction. In this case, the lack of any substantialsignal degradation can be used by the collision warning system todetermine that motor vehicle 102 does have line of sight with respect totarget vehicle 1002.

FIG. 12 illustrates an exemplary embodiment of a set of signalcharacteristics that can be used to estimate line of sight for a motorvehicle with respect to another vehicle. In different embodiments,different signal characteristics can be used for estimating line ofsight. The term “signal characteristic” as used throughout this detaileddescription and in the claims refers to any measurable characteristic ofan electromagnetic signal. Furthermore, the term “signal degradation”refers to any measurable change in one or more signal characteristics.It will be understood that the following signal characteristics areexemplary and are not meant to be limiting.

In some embodiments, line of sight estimation system 1200 includes firstsignal characteristic 1202, second signal characteristic 1204, thirdsignal characteristic 1206 and fourth signal characteristic 1208. In theexemplary embodiment, first signal characteristic 1202 is associatedwith the received signal strength index (RSSI) of a signal. The RSSI isa measurement of the power present in a received radio signal. In somecases, RSSI measurements may be unit-less in the range between 0 and255. In an exemplary embodiment, signal degradation associated with theRSSI can be computed by comparing a reference RSSI stored in memory, asa function of distance to the transmitting vehicle, to a measured RSSIof the actual transmission. If the actual RSSI is substantially belowthe reference RSSI value, the collision warning system may assume nonline of sight conditions due to an obstruction blocking the signal orotherwise reflecting the signal. If, however, there is no substantialdegradation between the measured RSSI and the reference RSSI, thecollision warning system can assume there is line of sight.

Second signal characteristic 1204 may be associated with the packetsuccess ratio (PSR) of a signal. The PSR may be a measure of the numberof packets received divided by the total number of packets transmitted.In some cases, the PSR ratio may be given as a percentage or as afraction between 0 and 1. In an exemplary embodiment, signal degradationassociated with the PSR can be computed by comparing a reference PSRvalue stored in memory, as a function of distance to the transmittingvehicle, with a measured PSR of the actual transmission. If the measuredPSR value is substantially below the reference PSR value, the collisionwarning system may assume non line of sight conditions due to anobstruction blocking the signal or otherwise reflecting the signal. If,however, there is no substantial degradation between the measured PSRand the reference PSR, the collision warning system can assume there isline of sight.

Third signal characteristic 1206 may be associated with an antennadiversity correlation between two or more receiving antennas. Generally,the receiving antennas can be any types of antennas capable oftransmitting any types of signals. In one embodiment, the antennas maybe associated with other nodes of a vehicle communication network. Forunobstructed line of sight communication, the correlation between thesignals coming from the two receiving antennas (some distance apart) maybe stronger compared to obstructed line of sight communication. In anexemplary embodiment, signal degradation associated with antennadiversity correlation can be computed by comparing a reference antennadiversity correlation value stored in memory with a measured antennadiversity correlation value. If the measured antenna diversitycorrelation value is substantially below the reference antenna diversitycorrelation value, the collision warning system may assume non line ofsight conditions due to an obstruction blocking the signal or otherwisereflecting the signal. If, however, there is no substantial degradationbetween the measured antenna diversity correlation and the referenceantenna diversity correlation, the collision warning system can assumethere is line of sight.

Fourth signal characteristic 1208 may be associated with the first powercomponent (FPC) of the signal. The FPC characteristic of a signal may besimilar to the RSSI of the signal, except that the RSSI is an average ofthe entire packet, while the FPC is the first reading of the packet. Inan exemplary embodiment, signal degradation associated with the FPC canbe computed by comparing a reference FPC value stored in memory, as afunction of distance to the transmitting vehicle, with a measured FPC ofthe actual transmission. If the measured FPC value is substantiallybelow the reference FPC value, the collision warning system may assumenon line of sight conditions due to an obstruction blocking the signalor otherwise reflecting the signal. If, however, there is no substantialdegradation between the measured FPC and the reference FPC, thecollision warning system can assume there is line of sight.

In this embodiment, first signal characteristic 1202, second signalcharacteristic 1204, third signal characteristic 1206, and fourth signalcharacteristic 1208 are illustrated as inputs to line of sightestimation unit 1210. Generally, any combination of input signalcharacteristics can be used. In some cases, only a single signalcharacteristic may be used for estimating line of sight. In other cases,more than one signal characteristic can be used for estimating line ofsight. For example, in another embodiment, a line of sight estimationunit may utilize both RSSI and PSR in determining line of sightconditions. In still other cases, four signal characteristics can beused for estimating line of sight.

FIG. 13 illustrates an exemplary embodiment of a general process fordetermining line of sight according to a particular signalcharacteristic. In particular, the process illustrated here may beapplied to many different signal characteristics. In this embodiment,the following steps may be performed by ECU 120; however in someembodiments these steps may be performed by additional systems ordevices associated with motor vehicle 102 and/or collision warningsystem 100. In addition, it will be understood that in other embodimentsone or more of the following steps may be optional.

During step 1302, ECU 120 may establish a connection with a targetvehicle using a vehicle communication network. Next, during step 1304,ECU 120 may calculate the position of a target vehicle according toinformation received using the vehicle communication network. Forexample, in many cases vehicles may transmit current GPS locations.Following step 1304, ECU 120 may calculate or otherwise determine thelocation of motor vehicle 102, also referred to as the subject vehicle,using information from a GPS receiver, during step 1306. Next, duringstep 1308, ECU 120 may calculate the relative distance between thetarget vehicle and motor vehicle 102.

Following step 1308, ECU 120 may proceed to step 1310. During step 1310,ECU 120 may calculate one or more measured signal characteristics. Forexample, ECU 120 may calculate RSSI, PSR, PDSD and/or FPC, as well asany other measured signal characteristic. Next, during step 1312, ECU120 can retrieve the reference signal characteristics as a function ofthe vehicle distance which was calculated during step 1308. Thereference signal characteristics will generally be associated with thetype of measured signal characteristics. In other words, if the measuredsignal characteristics include an RSSI value, ECU 120 will retrieve areference RSSI value. Likewise, ECU 120 will retrieve a reference PSRvalue for when the measured signal characteristics include a PSR value.

Generally, ECU 120 may use any method for retrieving reference signalcharacteristics. In some cases, ECU 120 may retrieve the referencesignal characteristics as a function of distance to the target vehicle,which was computed during step 1308. This configuration allows for amore accurate comparison to the measured signal characteristics, sincesome signal degradation occurs with distance even without line of sightobstructions.

At this point, ECU 120 may proceed to step 1314, where the measuredsignal characteristics are compared with the reference signalcharacteristics. Following step 1314, ECU 120 may proceed to step 1316.During step 1316, ECU 120 may determine if the measured signalcharacteristics are substantially degraded according to the comparisonmade during step 1314. If, during step 1316, ECU 120 determines that themeasured signal characteristics are not substantially degraded then ECU120 may proceed to step 1318, where it is determined that the driver ofmotor vehicle 102 has line of sight. Otherwise, ECU 120 may proceed tostep 1320, where it is determined that the driver of motor vehicle 102does not have line of sight.

It will be understood that in embodiments using multiple signalcharacteristics to determine line of sight, it may be possible that somesignal characteristics are substantially degraded while other signalcharacteristics are not substantially degraded. In such embodiments, theoverall determination of signal characteristic degradation performedduring step 1316 can be accomplished by weighting various signalcharacteristics.

In the preceding discussion, examples of objects that may obstruct theview of a driver have included vehicles and buildings. However, it willbe understood that the provisions for determining line of sightconditions discussed above are not limited to use with any particulartype of obstruction. In particular, since any obstructing object maytend to degrade a signal received from a target vehicle, line of sightconditions can be determined using these methods for any type ofobstructions.

FIGS. 14 and 15 illustrate an embodiment of another method fordetermining line of sight using information received from a vehiclecommunication network. Referring to FIGS. 14 and 15, motor vehicle 102is disposed behind intermediate vehicle 1402. In an exemplaryembodiment, intermediate vehicle 1402 is a truck. In this case, the lineof sight of motor vehicle 102 is obstructed by intermediate vehicle1402. In particular, target vehicle 1404 cannot be seen by a driver ofmotor vehicle 102.

In cases where line of sight may be obstructed by an intermediatevehicle, a collision warning system can include provisions fordetermining if a driver has line of sight of a target vehicle usinginformation received from the intermediate vehicle. Referring to FIG.14, motor vehicle 102 may receive information from intermediate vehicle1402 by way of vehicle communication network 1450, such as a DSRCnetwork. In some cases, motor vehicle 102 may receive the position ofintermediate vehicle 1402. In addition, motor vehicle 102 may be incommunication with target vehicle 1404 using vehicle communicationnetwork 1450 as well.

After receiving information from intermediate vehicle 1402, collisionwarning system 100 may determine a headway distance H1 between a frontend of motor vehicle 102 and a rearward end of intermediate vehicle1402. In some cases, headway distance H1 can be estimated using only theposition of intermediate vehicle 1402. In other cases, headway distanceH1 can be more accurately determined using additional informationreceived from intermediate vehicle 1402 by way of vehicle communicationnetwork 1450, including, for example, the length of intermediate vehicle1402.

At this point, collision warning system 100 can estimate line of sightaccording to headway distance H1. In particular, referring to FIG. 14,since headway distance H1 is relatively small, collision warning system100 determines that intermediate vehicle 1402 is close to motor vehicle102. In this situation, collision warning system 100 may assumeintermediate vehicle 1402 obstructs the view of motor vehicle 102. Inother words, collision warning system 100 determines that there is notline of sight to target vehicle 1404. In contrast, in the situationillustrated in FIG. 15, since headway distance H2 is relatively large,collision warning system 100 determines that intermediate vehicle 1402is far ahead from motor vehicle 102. In this situation, collisionwarning system 100 may assume intermediate vehicle 1402 is notsubstantially obstructing the view of motor vehicle 102. In other words,collision warning system 100 determines that there is good line of sightto target vehicle 1404. With this arrangement, a collision warningsystem can estimate line of sight conditions by determining the headwaydistance between a subject vehicle and an intermediate vehicle thatmight potentially obstruct the view of a target vehicle.

In another embodiment, a collision warning system may include provisionsfor determining if an intermediate vehicle is obstructing the view of asubject vehicle using information related to a size of the intermediatevehicle. Referring to FIG. 16, intermediate vehicle 1602, in the form ofa truck, is disposed just in front of motor vehicle 102. In this case,the large size of intermediate vehicle 1602 obstructs the view of motorvehicle 102. In particular, a driver within motor vehicle 102 is unableto see target vehicle 1604 because of truck 1602. In contrast, referringto FIG. 17, intermediate vehicle 1702, in the form of a small coupe, isalso disposed just in front of motor vehicle 102. In this case,intermediate vehicle 1702 does not significantly obstruct the view ofmotor vehicle 102 due to the small size of intermediate vehicle 1702.

In some cases, collision warning system 100 may be configured to receiveinformation related to the size of an intermediate vehicle. Referring toFIG. 16, collision warning system 100 receives information related tothe width of intermediate vehicle 1602 by way of vehicle communicationnetwork 1650. In particular, intermediate vehicle 1602 is determined tohave a width W1. Since width W1 is relatively large for a vehicle,collision warning system 100 determines that intermediate vehicle 1602is obstructing the view of motor vehicle 102. In other words, collisionwarning system 100 determines that motor vehicle 102 does not have lineof sight of target vehicle 1604.

In contrast, referring to FIG. 17, collision warning system 100 receivesinformation about the width of intermediate vehicle 1702. In particular,intermediate vehicle 1702 is determined to have a width W2. Since widthW2 is relatively small for a vehicle, collision warning system 100determines that intermediate vehicle 1702 is not obstructing the view ofmotor vehicle 102. In other words, collision warning system 100determines that motor vehicle 102 has good line of sight of targetvehicle 1604.

It will be understood that a collision warning system can make use of acombination of various types of information to determine if a subjectvehicle has good line of sight of a target vehicle when an intermediatevehicle is present. In some embodiments, a collision warning system cancombine information including headway distance between a subject vehicleand an intermediate vehicle, intermediate vehicle size, and targetvehicle location to determine if the target vehicle is within the lineof sight of the subject vehicle.

For example, referring to FIGS. 16 and 17, collision warning system 100can estimate visible region 1640 and non-visible region 1642 using thelocations of motor vehicle 102 and intermediate vehicle 1602, as well asan estimated size for intermediate vehicle 1602. Furthermore, using thelocation of target vehicle 1604, collision warning system 100 candetermine if target vehicle 1604 is within visible region 1640 ornon-visible region 1642. If target vehicle 1604 is determined to bewithin non-visible region 1642, as seen in FIG. 16, then motor vehicle102 does not have line of sight of target vehicle 1604. If, however,target vehicle 1604 is determined to be within visible region 1640, asseen in FIG. 17, then motor vehicle 102 does have line of sight oftarget vehicle 1604.

FIG. 18 illustrates an embodiment of a process for determining line ofsight conditions according to headway distance between a subject vehicleand an intermediate vehicle. In this embodiment, the following steps maybe performed by ECU 120; however in some embodiments these steps may beperformed by additional systems or devices associated with motor vehicle102 and/or collision warning system 100. In addition, it will beunderstood that in other embodiments one or more of the following stepsmay be optional.

During step 1802, ECU 120 may receive information related to a locationof an intermediate vehicle. In some cases, the information can bereceived using a vehicle communication network. Next, during step 1804,ECU 120 may retrieve a current location for motor vehicle 102. In somecases, ECU 120 may receive information from a GPS receiver to determinethe current location. Following this, during step 1806, ECU 120 maycalculate a headway distance between motor vehicle 102 and theintermediate vehicle. Next, during step 1808, ECU 120 may retrieve apredefined headway distance.

After step 1808, ECU 120 may proceed to step 1810. During step 1810, ECU120 may compare the current headway distance with the predefined headwaydistance. If the current headway distance is less than the predefinedheadway distance, then ECU 120 may proceed to step 1812, where it isdetermined that a driver does not have line of sight. Otherwise, ECU 120may proceed to step 1814, where it is determined that a driver has goodline of sight.

FIG. 19 illustrates an embodiment of a process for determining line ofsight conditions according to a size of an intermediate vehicle. In thisembodiment, the following steps may be performed by ECU 120; however insome embodiments these steps may be performed by additional systems ordevices associated with motor vehicle 102 and/or collision warningsystem 100. In addition, it will be understood that in other embodimentsone or more of the following steps may be optional.

During step 1902, ECU 120 may receive information related to the size ofan intermediate vehicle. In some cases, the size could include a width,a length and a height. In other cases, only one dimension could bereceived. In still other cases, ECU 120 may receive a class of theintermediate vehicle, such as “truck,” “sedan,” “coupe,” “motorcycle” aswell as other classes of vehicles. Using this information, ECU 120 mayestimate one or more dimensions of the intermediate vehicle according tothe vehicle class.

Next, during step 1904, ECU 120 may retrieve a predetermined vehiclesize. Following this, ECU 120 may proceed to step 1906. During step1906, ECU 120 may determine if the intermediate vehicle size is lessthan the predefined vehicle size. If so, then ECU 120 may proceed tostep 1908, where it is determined that the driver has good line ofsight. Otherwise, ECU 120 may proceed to step 1910, where it isdetermined that the driver does not have line of sight.

Although the intermediate vehicle in the discussion above is a vehiclepositioned in front of a subject vehicle, it will be understood that inother embodiments these provisions could be used for an intermediatevehicle positioned in any location between a subject vehicle and atarget vehicle. For example, the methods discussed above could also beapplied to situations in which an intermediate vehicle is disposed infront of a target vehicle, rather than a subject vehicle. Furthermore,these provisions can be applied to both stationary and movingintermediate vehicles. Still more, the method discussed above can beused with multiple intermediate vehicles, rather than just a singlevehicle.

While various embodiments of the invention have been described, thedescription is intended to be exemplary, rather than limiting and itwill be apparent to those of ordinary skill in the art that many moreembodiments and implementations are possible that are within the scopeof the invention. Accordingly, the invention is not to be restrictedexcept in light of the attached claims and their equivalents. Also,various modifications and changes may be made within the scope of theattached claims.

What is claimed is:
 1. A method of operating a collision warning system in a motor vehicle, comprising the steps of: receiving information related to a target vehicle; determining if the target vehicle is in a line of sight of the motor vehicle; the collision warning system including multiple alert modes; operating the collision warning system in a normal alert mode when the target vehicle is in the line of sight of the motor vehicle; operating the collision warning system in an enhanced alert mode when the target vehicle is not in the line of sight of the motor vehicle; and wherein the normal alert mode is different than the enhanced alert mode.
 2. The method according to claim 1, wherein the step of determining if the target vehicle is in the line of sight of the motor vehicle further includes the steps of: receiving a measured signal characteristic from a signal transmitted by the target vehicle; retrieving a reference signal characteristic; and determining a line of sight condition for the motor vehicle with respect to the target vehicle using the measured signal characteristic and the reference signal characteristic.
 3. The method according to claim 1, wherein the step of determining if the target vehicle is in the line of sight of the motor vehicle further includes the steps of: receiving information related to the target vehicle; receiving information related to an intermediate vehicle; and determining if the intermediate vehicle obstructs the line of sight between the motor vehicle and the target vehicle.
 4. The method according to claim 1, wherein the step of operating the collision warning system further includes the steps of: determining that the collision warning system is operating in the normal alert mode; calculating a threat level, the threat level being associated with a threat of collision between the motor vehicle and the target vehicle and wherein the threat level is associated with a first threat level and a second threat level that is higher than the first threat level; issuing a warning alert when the threat level is the second threat level; and issuing no alert when the threat level is the first threat level.
 5. The method according to claim 1, wherein the step of operating the collision warning system further includes the steps of: determining that the collision warning system is operating in the enhanced alert mode; calculating a threat level, the threat level being associated with a threat of collision between the motor vehicle and the target vehicle and wherein the threat level is associated with a first threat level and a second threat level that is higher than the first threat level; issuing a warning alert when the threat level is the second threat level; and issuing an informing alert when the threat level is the first threat level.
 6. The method according to claim 1, wherein the normal alert mode is associated with a warning alert only and wherein the enhanced alert mode is associated with an informing alert and a warning alert.
 7. A method of operating a collision warning system in a motor vehicle, comprising the steps of: receiving a signal transmitted by a target vehicle; determining a measured signal characteristic from the signal transmitted by the target vehicle; retrieving a reference signal characteristic corresponding to the measured signal characteristic; determining a line of sight condition for the motor vehicle with respect to the target vehicle using the measured signal characteristic and the reference signal characteristic; operating the collision warning system in a normal alert mode when the target vehicle is in the line of sight of the motor vehicle; operating the collision warning system in an enhanced alert mode when the target vehicle is not in the line of sight of the motor vehicle; and wherein the normal alert mode is different than the enhanced alert mode.
 8. The method according to claim 7, wherein the measured signal characteristic is a received signal strength index of the signal.
 9. The method according to claim 7, wherein the measured signal characteristic is a packet success ratio of the signal.
 10. The method according to claim 7, wherein the measured signal characteristic is a first power component of the signal.
 11. The method according to claim 7, wherein the measured signal characteristic is associated with a correlation between two or more receiving antennas.
 12. The method according to claim 7, wherein the measured signal characteristic is associated with a plurality of measured signal characteristics.
 13. The method according to claim 7, wherein the number of alerts issued in the enhanced alert mode is greater than the number of alerts issued in the normal alert mode.
 14. The method according to claim 7, wherein the measured signal characteristic, the reference signal characteristic and a distance to the target vehicle are used to determine the line of sight condition for the motor vehicle with respect to the target vehicle.
 15. A method of operating a collision warning system in a motor vehicle, comprising the steps of: receiving information related to a target vehicle; receiving information related to an intermediate vehicle; determining if the intermediate vehicle obstructs the line of sight between the motor vehicle and the target vehicle; operating the collision warning system in a normal alert mode when the target vehicle is in the line of sight of the motor vehicle; and operating the collision warning system in an enhanced alert mode when the target vehicle is not in the line of sight of the motor vehicle.
 16. The method according to claim 15, wherein the step of determining if the intermediate vehicle obstructs the line of sight further includes the steps of: receiving information related to a location of the intermediate vehicle; calculating a headway distance between the motor vehicle and the intermediate vehicle; retrieving a predetermined headway distance; determining that the intermediate vehicle does not obstruct the line of sight between the motor vehicle and the target vehicle when the headway distance is greater than the predetermined headway distance; and determining that the intermediate vehicle does obstruct the line of sight between the motor vehicle and the target vehicle when the headway distance is less than the predetermined headway distance.
 17. The method according to claim 15, wherein the step of determining if the intermediate vehicle obstructs the line of sight further includes the steps of: receiving information related to a vehicle size of the intermediate vehicle; retrieving a predetermined vehicle size; determining that the intermediate vehicle does not obstruct the line of sight between the motor vehicle and the target vehicle when the vehicle size is less than the predetermined vehicle size; and determining that the intermediate vehicle does obstruct the line of sight between the motor vehicle and the target vehicle when the vehicle size is greater than the predetermined vehicle size.
 18. The method according to claim 17, wherein the step of receiving information related to the vehicle size includes a step of receiving a vehicle type of the intermediate vehicle and estimating the vehicle size according to the vehicle type.
 19. The method according to claim 17, wherein the vehicle size is associated with a vehicle width.
 20. The method according to claim 15, wherein the line of sight of the motor vehicle with respect to the target vehicle is determined using a headway distance from the motor vehicle to the intermediate vehicle and an estimated width of the intermediate vehicle. 